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KVM: s390: Increase size of union sca_utility to four bytes

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kvm_s390_update_topology_change_report() modifies a single bit within
sca_utility using cmpxchg(). Given that the size of the sca_utility union
is two bytes this generates very inefficient code. Change the size to four
bytes, so better code can be generated.

Even though the size of sca_utility doesn't reflect architecture anymore
this seems to be the easiest and most pragmatic approach to avoid
inefficient code.

Acked-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Acked-by: Janosch Frank <frankja@linux.ibm.com>
Link: https://lore.kernel.org/r/20241126102515.3178914-4-hca@linux.ibm.com
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
This commit is contained in:
Heiko Carstens 2024-11-26 11:25:15 +01:00
parent 7061c63919
commit f93d6d62e4
1 changed files with 10 additions and 5 deletions
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15
arch/s390/include/asm/kvm_host.h
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@ -94,11 +94,16 @@ union ipte_control {
}; };
}; };
/*
* Utility is defined as two bytes but having it four bytes wide
* generates more efficient code. Since the following bytes are
* reserved this makes no functional difference.
*/
union sca_utility { union sca_utility {
__u16 val; __u32 val;
struct { struct {
__u16 mtcr : 1; __u32 mtcr : 1;
__u16 reserved : 15; __u32 : 31;
}; };
}; };
@ -107,7 +112,7 @@ struct bsca_block {
__u64 reserved[5]; __u64 reserved[5];
__u64 mcn; __u64 mcn;
union sca_utility utility; union sca_utility utility;
__u8 reserved2[6]; __u8 reserved2[4];
struct bsca_entry cpu[KVM_S390_BSCA_CPU_SLOTS]; struct bsca_entry cpu[KVM_S390_BSCA_CPU_SLOTS];
}; };
@ -115,7 +120,7 @@ struct esca_block {
union ipte_control ipte_control; union ipte_control ipte_control;
__u64 reserved1[6]; __u64 reserved1[6];
union sca_utility utility; union sca_utility utility;
__u8 reserved2[6]; __u8 reserved2[4];
__u64 mcn[4]; __u64 mcn[4];
__u64 reserved3[20]; __u64 reserved3[20];
struct esca_entry cpu[KVM_S390_ESCA_CPU_SLOTS]; struct esca_entry cpu[KVM_S390_ESCA_CPU_SLOTS];